The present invention relates to an evaporator suitable for use in a car air conditioner, which is a refrigeration cycle to be mounted on an automobile, for example.
In this specification and appended claims, the upper and lower sides of each drawing will be referred to as “upper” and “lower,” respectively.
An evaporator of such a type has been proposed (see Japanese Patent Application Laid-Open (kokai) No. 2009-156532). The proposed evaporator comprises a plurality of heat exchange tubes extending in the vertical direction, and upper and lower header portions to which upper and lower end portions of the heat exchange tubes are connected, respectively. There are provided upward flow tube groups each of which is formed by a plurality of heat exchange tubes spaced from one another in the longitudinal direction of the header portions and in which refrigerant flows through the heat exchange tubes from the lower side toward the upper side, and downward flow tube groups each of which is formed by a plurality of heat exchange tubes disposed at predetermined intervals in the longitudinal direction of the header portions and in which refrigerant flows through the heat exchange tubes from the upper side toward the lower side. The evaporator includes two tube rows juxtaposed in the air-passage direction, each tube row is formed by a plurality of tube groups spaced from one another in the longitudinal direction of the header portions. The leeward tube row includes three or more tube groups, and the windward tube row includes a plurality of tube groups the number of which is one less than the number of the tube groups of the leeward tube row. The flow direction of refrigerant in one of adjacent tube groups is opposite the flow direction of refrigerant in the other tube group. Upper and lower end portions of the heat exchange tubes of the leeward tube row and upper and lower end portions of the heat exchange tubes of the windward tube row are connected to the leeward upper and lower header portions and the windward upper and lower header portions, respectively. Each of the leeward upper and lower header portions has sections which are equal in number to the tube groups of the leeward tube row, and the heat exchange tubes of each tube group of the leeward tube row communicate with the corresponding section. Each of the windward upper and lower header portions has sections which are equal in number to the tube groups of the windward tube row, and the heat exchange tubes of each tube group of the windward tube row communicate with the corresponding section. A refrigerant inlet is provided at a section at one end of the leeward upper or lower header portion. A refrigerant outlet is provided on a windward upper or lower header portion corresponding to the leeward upper or lower header portion on which the refrigerant inlet is provided, such that the refrigerant outlet is provided at a section at one end of the windward upper or lower header portion located on the same side as the one end at which the refrigerant inlet is provided. The evaporator has upflow paths each formed by one upward flow tube group, and downflow paths each formed by at least one downward flow tube group. The upflow paths and the downflow paths are alternately disposed such that the final path becomes an upflow path or a downflow path. Refrigerant having flowed from the refrigerant inlet is caused to pass through all the paths and flow out from the refrigerant outlet. Refrigerant flows from the upper side toward the lower side through the heat exchange tubes of a farthest tube group of the leeward tube row which is farthest from the refrigerant inlet and through the heat exchange tubes of a farthest tube group of the windward tube row which is farthest from the refrigerant outlet. These two farthest tube groups form a single downflow path. A tube group located on the upstream side, with respect to the refrigerant flow direction, of the farthest tube group of the leeward tube row is an upward flow tube group. The upper header portion has a refrigerant inflow section which communicates with upper end portions of the heat exchange tubes of the upward flow tube group, and a refrigerant outflow section which communicates with upper end portions of the heat exchange tubes of the downward flow tube group located adjacent to and downstream of the upward flow tube group with respect to the refrigerant flow direction. The refrigerant inflow section and the refrigerant outflow section communicate with each other via an opening provided between the two sections such that the opening extends over the entire boundary between the two sections.
In general, an evaporator used in a car air conditioner is desired to be designed such that a discharged air temperature, which is the temperature of air jetted from air-passing clearances each formed between adjacent heat exchange tubes, is made uniform among various parts of the evaporator in order to improve the comfort within a compartment of a vehicle on which the car air conditioner is mounted. For making the discharged air temperature uniform, the diverging flows of refrigerant within the evaporator must be adjusted.
Incidentally, in the evaporator described in the publication, refrigerant having entered the evaporator via the refrigerant inlet partially evaporates in the above-described upward flow tube group and a tube group located upstream of the upward flow tube group with respect to the refrigerant flow direction. Therefore, two-phase refrigerant (having a gas phase component and a liquid phase component) flows into the refrigerant inflow section of the upper header portion which communicates with the upper end portions of the heat exchange tubes of the upward flow tube group.
However, the opening formed between the two sections such that the opening extends over the entire interface between the two sections establishes communication between the interior of the refrigerant inflow section of the upper header portion which communicates with upper end portions of the heat exchange tubes of the upward flow tube group, and the interior of the refrigerant outflow section of the upper header portion which communicates with upper end portions of the heat exchange tubes of the downward flow tube group located adjacent to and downstream of the upward flow tube group with respect to the refrigerant flow direction. Therefore, refrigerant having flowed into the refrigerant inflow section flows straight into the refrigerant outflow section. Thus, the refrigerant flows into the refrigerant outflow section without the gas phase component and the liquid phase component being mixed together. Accordingly, the liquid phase component flows, in a large amount, into the upstream-side heat exchange tubes of the downward flow tube group due to the influence of gravity, and the gas phase component becomes more likely to flow within the refrigerant outflow section toward the downstream side, whereby the gas phase component flows, in a large amount, into downstream-side heat exchange tubes of the downward flow tube group. As a result, the amount of refrigerant flowing through the heat exchange tubes of the downward flow tube group (serving as a downflow path) located downstream of the upward flow tube group (serving as an upflow path) with respect to the refrigerant flow direction becomes ununiform, whereby the discharged air temperature becomes ununiform among various portions of the evaporator.